Reactions of 2,3-Dichloro- and 2,3,5-Trichloro-4,4-ethylenedioxy-2-cyclopentenones with Some O-, S-, and N-Nucleophiles

2,3-Dichloro- and 2,3,5-trichloro-4,4-ethylenedioxy-2-cyclopentenones react with allyl and benzyl alcoholates and thiolates and benzylamine to give products resulting from Ad_NE substitution of the 3-chlorine atom, [1,3]-sigmatropic rearrangement, and cleavage of the C¹-C² bond.     

Nucleophilic addition of 2-(trimethylsilyloxy)furan to a d-glucopyranose oxocarbenium ion

Cp₂Zr(ClO₄)₂ was used as a promoter for nucleophilic addition of 2-(trimethylsilyloxy) furan (TMSOF) to 2,3,4,6-tetra-O-benzyl-d-glucopyranosyl fluoride to give a 2:1:1 mixture of adducts in 80% yield. NMR data and postulated transition states are consistent with a 3:1 ratio of regioisomers at C-5 and C-3 of TMSOF and a 2:1 ratio of threo and erythro α-adducts at C-5.     

A novel synthesis, including asymmetric synthesis, of 2,4,4-trisubstituted 2-cyclopentenones based on the reaction of 1-chlorovinyl p-tolyl sulfoxides with acetonitrile and its homologues

Reaction of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from chloromethyl p-tolyl sulfoxide and ketones in high overall yields, with cyanomethyllithium (lithium α-carbanion of acetonitrile) gave adducts in high to quantitative yields. The adducts were treated with LDA followed by lithium α-carbanion of the homologues of acetonitrile to give 3,5,5-trisubstituted enaminonitriles in good to high yields. Hydrolysis of the enaminonitriles under acidic conditions gave 2,4,4-trisubstituted 2-cyclopentenones in good yields. By using the optically active chloromethyl p-tolyl sulfoxide and unsymmetrical ketones, this procedure gave the optically pure 2,4,4-trisubstituted 2-cyclopentenones. The scope and limitations of this method and the mechanism of the reactions are also discussed. These procedures offer a new and effective method for the synthesis of 2,4,4-trisubstituted 2-cyclopentenones from four components, ketones, chloromethyl p-tolyl sulfoxide, acetonitrile, and its homologues.     

Cyclopentanones—XVI : Prostaglandin synthesis involving catalytic hydrogenation of 2,3-dialkyl-4-hydroxy-2-cyclopentenones

2,3-Dialkyl-4-hydroxy-2-cyclopentenones with differently functionalised side chains yield predominantly all-cis 2,3-dialkyl-1-4,-dihydroxycyclopentanes on catalytic hydrogenation. Epimerisation at C-12 (PG numbering) leads to prostaglandin synthons. Influence of the side-chain functions on these reactions is described.     

A novel synthesis of 2,4,4-trisubstituted 2-cyclopentenones by consecutive reaction of 1-chlorovinyl p-tolyl sulfoxides with acetonitrile and its homologues

1-Chlorovinyl p-tolyl sulfoxides were synthesized from several kinds of ketones and chloromethyl p-tolyl sulfoxide in three steps in high overall yields. Treatment of the 1-chlorovinyl p-tolyl sulfoxides with cyanomethyllithium (lithium α-carbanion of acetonitrile) at low temperature gave the adducts in almost quantitative yields. The adducts were then treated with LDA followed by excess lithium α-carbanion of the homologues of acetonitrile to afford 3,5,5-trisubstituted cyclopentadienyl enaminonitriles, which were hydrolyzed and heated under acidic conditions to give 2,4,4-trisubstituted 2-cyclopentenones in good overall yields.     

Photochemistry of 6-trifluoromethyl-4,4-dimethyl-2-cyclohexenone

The photochemical behaviour of the title compound, newly synthesized in four steps from 4,4-dimethylcyclohexanone, is compared to that of 4,4-dimethyl- and 4,4,6-trimethyl-2-cyclohexenone. All three enones undergo rearrangement to bicyclo[3.1.0]hexan-2-ones and 3-isopropyl-2-cyclopentenones in benzene, t.butanol and acentonitrile, but only the CF₃-enone is also reduced to the saturated ketone in the latter two solvents.     

Coupling of cyclopropylcarbene-chromium complex with ferrocenyl alkynes: synthesis of 5-ferrocenyl-5-hydroxy-2-cyclopentenones and 4-ferrocenyl-4-cyclopentene-1,3-diones

The coupling of ferrocenyl alkynes with cyclopropylcarbene-chromium complex leads to ferrocenyl-substituted 2-cyclopentenones with or without a hydroxy substituent, namely 4-cyclopentene-1,3-diones, 2-cyclobutenones, and α,β-unsaturated aldehydes in varying amounts. The reaction initially produces a cyclopentadienone intermediate, then to the double bond of which, bearing a ferrocenyl group, addition of water occurs to afford hydroxy-substituted 2-cyclopentenones. In all the products, the hydroxy group ends up α to the ferrocenyl moiety. In contrast, where no addition of water occurs, the alkenic bond is reduced to give 2-cyclopentenones. A secondary reaction product, namely 4-cyclopentene-1,3-dione, is formed by hydrolysis of the cyclopentadienone intermediates.     

Picolinyl group as an efficient alcohol protecting group: cleavage with Zn(OAc)2·2H2O under a neutral condition

As an efficient alcohol protecting group, picolinates (Pic), prepared from the corresponding alcohols using commercial picolinoyl chloride, are readily cleaved by Zn(OAc)₂ or Cu(OAc)₂, even in the presence of other common alcohol protecting groups. Moreover, the picolinyl group at C-2 position in carbohydrates can be selectively cleaved to give methyl 4,6-O-benzylidene-3-O-picolinyl-α-d-glucopyranoside and 3-O-picolinyl methyl-4,6-O-benzylidene-α-d-galactopyranoside in good yields.     

Stereocontrolled acylation of (η4-cycloheptatriene)iron tricarbonyl

The anion derived by deprotonating (cycloheptatriene)Fe(CO)₃ reacts with acid chlorides to give exo C-7 substitution. The acyl group is readily isomerized to C-5 on treatment with base. The C-7 acylated products can be deprotonated; the resulting anions react at oxygen with acyl chlorides and Me₃SiCl, and at carbon with MeI.     

A convenient synthesis of 1,2-difluoro-1, 2-dideoxyhexoses using xenon fluoride

A method for the addition of fluorine to the double bond in acetylated glycals using XeF₂ in the presence of BF₃ has been shown to provide a convenient route for the synthesis of acetylated 1, 2-dideoxy-1, 2-difluorosugars. The reagent attacks the double bond predominantly from the least hindered side to give a cis adduct, but the reaction also provided other isomers which have been separated by chromatography and their stereo-chemistry determined by ¹⁹F NMR spectroscopy. The proposed mechanism of the reaction involves an initial electrophilic attack by the reagent on C-2 followed by a nucleophilic attack on C-1. Deacetylation of the adducts gave 1, 2-dideoxyl-1, 2-difluorosaccharides, which are of interest in biochemical studies. A crystalline 2-deoxy-2-l-fucose was prepared by selective hydrolysis of the anomeric fluorine atom of 1, 2-dideoxy-1, 2-difluoro-l-fucose.     

Selective reduction of 1,4-diarylimidazoline-3-oxides to imidazolidin-1-ols and hydroxylamine derivatives

Abstract  

C-2-unsubstituted imidazoline-3-oxides were reduced with NaBH₄ in THF to give the corresponding trans-3,5-diarylimidazolidin-1-ols, while under the same conditions C-2-substituted derivatives gave the corresponding ring–chain–ring tautomers. Treatment of the crude reaction mixture from the reduction of C-2-unsubstituted imidazoline-3-oxides with a MeOH–H₂O mixture provided reductive C–N bond cleavage to give hydroxylamines, while under the same conditions ring–chain–ring tautomers remained unchanged.     

Maximization of yield of C-13 isotope by multiphoton dissociation of Freon-22 using high average power TEA CO2 laser

Selective multi-photon dissociation (MPD) of Freon-22 (CF₂HC1) molecules has been carried out using a TEA CO₂ laser at various CO₂ laser lines (9P(20)-9P(26)) in order to maximize the yield of C-13 isotope in the product (C₂F₄) at an enrichment factor of 100. The effects of laser pulse tail due to the presence of N₂ in the laser mixture on the enrichment factor and yield of C-13 are investigated. It is found that the addition of a small amount of N₂ is possible in the laser mixture without a significant drop in the yield at desired enrichment factor. Addition of a small amount of N₂ improves the laser efficiency considerably. At a given pulse energy, a slight change in the near field intensity distribution of a laser severely affects the selectivity of C-13 isotope. The computed far-field intensity distributions of the measured near-field intensities show marked spatial variation in the focal spots that leads to a drop in selectivity. For macroscopic production of C-13 isotope a simple and novel multi-pass cavity has been designed and tested to focus the energy repeatedly keeping the optimum fluence constant at each focal spot.     

The high resolution mass spectrum of 2-acetamido-1,3,4,6-tetra-O-acetyl-2-deoxy-α-D-glucopyranose

2-Acetamido-1,3,4,6-tetra-O-acetyl-2-deoxy-α-D-glucopyranose (I), and its analogs specifically mono (trideuterioacetylated) at O-1 (III), at N-2 (II), at O-4 (IV) and at O-6 (V), have been examined by high-resolution mass spectrometry. From the elemental compositions of the fragment ions, the mass-number shifts resulting from deuterium incorporation and analysis of metastable transitions, it has been possible to specify in detail the fragmentation pathways undergone by this molecule. The principal degradations of I proceed by initial rapid decomposition of the molecular ion (whose intensity is insignificant) by three routes: (i) by loss of the C-1 acetoxyl group as a radical to give the glycosyl cation (a), (ii) by loss of the 1-acetyl group as a radical to give an acyclic ion m/e 346 (b) and (iii) by loss of a C-6 fragment and acetic acid derived from the 3-acetate group to give m/e 241 (c).     

A novel fragmentation of trimethylsilyl ethers of 3β-hydroxy-Δ5-steroids

An ion formed by loss of 56 mass units from the molecular ion is often seen in mass spectra of trimethylsilyl ethers of C₁₉ and C₂₁ steroids having a 3β-hydroxy-Δ⁵ structure and an oxo group at C-17 or C-20. The nature of this fragment was investigated by the use of perdeuteriotrimethylsilyl ether derivatives and of [4-¹⁴C], [3-¹⁸O], [4,4-²H₂] and [2,2,4,4-²H] labelled derivatives of 3β-hydroxy-5-androsten-17-one and 3β-hydroxy-5-pregnen-20-one. Evidence is presented to show that the neutral fragment of mass 56 is composed of carbon atoms 1, 2 and 3, the oxygen at C-3 and four hydrogen atoms. During the fragmentation process, the trimethylsilyl group and one of the hydrogens at C-2 are transferred to the fragment that carries the charge.     

Acylation des acetyleniques selon friedel-crafts-I: Nouvelles syntheses d'alkylidene-cyclopentenones et de chlorocyclopentenones par rearrangements de carbocations

Unsaturated acid chlorides react with mono- and di-substituted alkynes to give a mixture of linear (unsaturated β-chlorovinylketones- and β-chloroallylketones), and cyclic (chloro-5-cyclopentenones and alkylidene-4-cyclopentenones) compounds. These derivatives are produced via carbonium ion rearrangements which result from the first step of the acylation. Experimental conditions and reagent structure exert a strong influence on the orientation of the transpositions. These rearrangements provide a good synthesis of alkylidene-4 cyclopentenones.     

Synthesis of 2-hydroxy-3-indolinones and 3-hydroxy-2-indolinones by anionic cyclization, in situ oxidation and rearrangement

Lithiation with butyllithium of 2-(benzylamino)benzamides (N-benzyl anthranilamides) occurs at the benzylic position to give an α-amino-organolithium that cyclizes to the 3-indolinone (indoxyl) ring (similar to a Parham cyclization). Autoxidation in air gives 2-hydroxy-3-indolinones. In the absence of a proton source, rearrangement of the aryl group from C-2 to C-3 occurs to give the 3-hydroxy-2-indolinone (oxindole) ring.     

Biosynthesis of fomannosin. 2H NMR evidence against postulated hydride shifts

²H NMR analysis of fomannosin (1) derived from [5,5-²H₂]-mevalonate established the presence of deuterium at C-5 and C-10, whereas no isotope was located at C-12.     

The reaction of trifluoromethanesulfenyl chloride with enamines of β-keto carboxylic acid anilides

1-Morpholino-cyclopenten-2-carboxylic acid anilides react with CF₃SCl in molar ratio 1:2 to give products of the displacement of two hydrogen atoms at C-2 and C-5. The analogous reaction with enamines of cyclohexanono- and cycloheptanono- 2-carboxylic acid anilides and benzoylacetanilides proceeds in 1:1 molar ratios affording enamines and keto compounds.     

Mass spectrometric decomposition processes of 2-methyl-1-hexene

Unimolecular decompositions of 2-methyl-1-hexene and several labelled analogues were studied following 70 eV electron impact (normal and metastable spectra) and field ionization (field ionization kinetic measurements). Molecules labelled with ¹³C in the 1-position and the methyl position were found to behave essentially identically. This is attributed to rapid transfer of a hydrogen atom mainly from C-5 to C-1 (γ-hydrogen shift). Loss of ethene, propene or propenyl do not involve loss of the methyl carbon or C-1. All three reactions are better than 90% specific in this respect under all conditions studied. At shorter times, C₃H₆ loss is the dominant reaction, while at longer times C₂H₆ loss accounts for >90% of the ion current. It is proposed that at least two distinct pathways for C₂H₄ loss operate in linear 1-alkenes, one of which (loss of carbons 1 and 2) is blocked by a 2-methyl substituent. The [C₆H₁₁]^+˙ and [C₅H₁₀]^+˙ ions formed from ¹³C labelled 2-methyl-1-hexenes fragment in an essentially statistical fashion.     

Déplacements chimiques induits en RMN par un réactif lanthanidique: I—Application á l'analyse conformationnelle de sulfites cycliques

The chemical shifts induced by Eu(fod)₃ in several series of 6-membered cyclic sulfites give the parameters K_c and Δ_SR of the complexation equilibrium for an assumed 1:1 stoicheiometry. The equilibrium constant K_c decreases with increasing bulk of the C-4 and C-6 substituents and polarity of the C-5 substituent, which corresponds to the increase of the i.r. stretching frequency vS?O. Thus axial S?O will be more tightly complexed than equatorial S?O. It can be predicted that when a conformational equilibrium exists without shift reagent, displacement towards an axial S?O form will occur with the reagent. Use of the Δ_SR pseudocontact equation confirms the following: (i) ax S?O chair forms are stabilized; (ii) eq S?O chairs with two eq C-4 and C-6 substituents show an equilibrium with a few percent of the ax S?O flexible conformation, particularly in the absence of an ax C-5 substituent; (iii) twist forms with a 2–5 axis, intermediate S?O and trans-4, 6-di-tert-Bu substituents give a boat form with O at the prow and ax S?O; (iv) the conformational equilibrium of trans-5-tert-butyl-2-oxo-1, 3, 2-dioxathiane (chair with ax tert-Bu and S?O ? 70%) is completely displaced towards that form; (v) cis-4,4,6-trimethyl-2-oxo-1,3,2-dioxathiane, which exists as an equilibrium in which the three types of S?O occur, is complexed essentially in the twist form with a 1–4 axis and ax S?O. Most of these results are supported by the coupling constants analysis for the ratio R₀/S₀ = 1.